1. Field of the Invention
The present invention relates to an oil pan of foamed resin and a method of fabrication thereof.
2. Description of the Related Art
An oil pan, for storing the lubricant to cool and lubricate the interior of an internal combustion engine of automotive vehicles, is arranged under the cylinder block of the internal combustion engine. An oil pan of metal has conventionally been used for strength and rigidity. With the recent advent of a resin having a sufficient strength and rigidity, however, a resin oil pan has been proposed (Japanese unexamined Patent Publication No. 7-27016).
The resin oil pan described in Japanese Unexamined Patent Publication No. 7-27016 is light in weight compared with a metal oil pan and, therefore, can reduce the weight of the internal combustion engine as a whole. Also, the resin oil pan has higher heat insulation properties than the metal oil pan and, therefore, can suppress the discharge of heat of the lubricant in the resin oil pan. Therefore, the temperature of the lubricant can be conveniently increased rapidly in starting the engine from the cold state, for example.
An oil pan of foamed resin has been proposed as a resin oil pan. The foamed resin oil pan has a high heat insulating effect and therefore can strongly suppress the discharge of heat from the lubricant in the oil pan. Further, the foamed resin oil pan has a high sound insulating effect, and can isolate noise generated in the internal combustion engine.
Nevertheless, the foamed resin poses the problem of a reduced rigidity as the result of foaming the resin. Especially, in mounting the oil pan in a liquid-tight fashion on the cylinder block of the internal combustion engine, the flange portion of the oil pan requires a high rigidity. The oil pan made of foamed resin in its entirety, however, has a reduced rigidity at the flange portion so that the lubricant would leak from between the cylinder block and the flange portion of the oil pan.
Accordingly, it is an object of this invention to provide an oil pan having high sound insulation properties and high heat insulation properties while at the same time maintaining the required strength and rigidity, and a method of fabricating the oil pan.